python中通过日期转换函数把字符串格式的日期转换成datetime格式的日期格式
time.strptime() converts the string to a struct_time tuple.
time.mktime() converts this tuple into seconds (elasped since epoch, C-style).
datetime.fromtimestamp() converts the seconds to a Python datetime object.

>>> import datetime,time
>>> stringDate = "2006-05-18 19:35:00"
>>> dt = datetime.datetime.fromtimestamp(time.mktime(time.strptime(stringDate,"%Y-%m-%d %H:%M:%S")))
>>> print dt
2006-05-18 19:35:00
>>> print type(dt)
<type 'datetime.datetime'>
>>>